1. Field of the Invention
This invention relates to improved rotating elements especially useful for transmitting forces, and for sustaining axial and torque bearing forces.
2. Prior Art
Conventional rotating elements intended for transmission of forces such as rotors or drive shafts are generally made of metal since these metal rotors or drive shafts are believed generally to posses great durability. More recently, however, there has been a considerable interest in reducing the weight of such rotating elements, particularly in vehicles, thereby increasing the fuel efficiencies at which those elements are driven. Thus, the design of a rotor or drive shaft of lighter weight has gained considerable interest from a fuel efficiency viewpoint. However, the design of a rotor or drive shaft, not only of lighter weight but also of greater axial stiffness, additionally would permit the use of such shaft in higher critical speed environments than presently possible with an all metal shaft.
In the past, some attempts have been made to design a lighter drive shaft. For example, it is known to reinforce metal tubes with helically wound filaments which are subsequently impregnated with a resin such as an epoxy resin, thereby forming a composite structure which has a metal portion and a plastic portion reinforced with continuous filament windings. Composite structures of this type have been capable of withstanding high circumferential speeds; however, they suffer from other disadvantages. For example, such helically wound rotors have inadequate axial stiffness for drive shaft applications.
As is pointed out in copending application Ser. No. 801,028, filed May 27, 1977, in order to get the requisite performance from a rotor or drive shaft which is fabricated from both a fiber-reinforced resin and a tubular metal shaft, the two essential load bearing materials, i.e. the metal and the fiber, must be combined in such a way as to operate harmoniously in adsorbing and transmitting substantial torsion and bending loads. Accordingly, improved tubular composites for transmitting torsion and bending loads are disclosed in the aforementioned patent application in which the axial loads primarily are borne by unidirectional reinforcing fiber filaments. These fiber filaments are embedded in a resin matrix. The primary torque loads are borne by a metal tube. The metal and fibers provide a composite structure in which the fibers are oriented at a predetermined angle of orientation so as to compensate for the significant differences in the physical properties of the fiber-reinforced resin and the physical properties of the metal tube, such as, for example, the difference in the thermal coefficient of expansion of the metal tube and the thermal coefficient of expansion of fiber of the fiber-reinforced resin. Thus, in the aforementioned patent application, there is described a tubular composite structure which comprises a metal tubular core, preferably of aluminum, having a layer of structural metal adhesive on the exterior surface of the metal core. On top of the structural adhesive layer are alternating laminae of resin-impregnated unidirectional reinforcing fibers, particularly carbon or graphite fibers, and of woven fiberglass, beginning with a layer of woven fiberglass followed by a lamina of resin-impregnated continuous unidirectional reinforcing fibers and continuing in alternating fashion but ending with a final layer of resin-impregnated continuous unidirectional reinforcing fibers. Each successive layer of resin-impregnated continuous unidirectional reinforcing fibers has the fibers oriented at an angle of between about 5.degree. to 20.degree. with respect to the longitudinal axis of the metal tube and in opposite orientation with respect to the next preceding layer. Such a tube is fabricated by preferentially wrapping around the metal core a generally quadrangular laminate of such fiber-reinforcing materials so as to provide a substantially cylindrical composite shaft having a uniform thickness of fiber-reinforced resin on the surface of the core.